By way of non-limiting example and in order to provide a background to the present invention reference is made to the field of extracorporeal blood treatment.
As it is well known in the art, blood treatment apparatus, such as hemodialysis machines, are used to continuously remove impurities from a patient's blood. The blood is typically pumped through tubes and moved through arterial and/or venous bubble traps (air separators) associated to disposable tubing sets connecting the patient to a dialyzer or other treatment unit mounted on the hemodialysis machine.
U.S. Pat. No. 4,263,808 discloses a one-piece hydraulic circuit that includes arterial and venous bubble trap chambers in which blood enters at entrances above the bottoms of the chambers and leaves near the bottoms of the chambers. Pressure in the chambers can be determined by transducers placed against impermeable latex membranes covering holes communicating with upper portions of the chambers.
U.S. Pat. No. 4,666,598 discloses a fluid flow chamber cassette that can be mounted with either its front wall or rear wall against a supporting machine, such as a hemodialysis machine, and has a flexible tube that extends from a sidewall and forms a loop that is symmetrical about a loop axis that is transverse to the side wall so that the loop will be acted upon by a pump roller on the machine both when the front wall is against the machine and when the rear wall is against the machine. The orientation of the cassette and the direction of fluid flow through the cassette can thus be changed by simply changing whether the front or the rear wall is mounted against the machine. The cassette comprises an arterial chamber and a venous chamber. The arterial chamber inlet enters the arterial chamber at a position higher than the arterial chamber outlet, and the venous chamber inlet enter the venous chamber at a position higher than the venous chamber outlet. When priming by causing reverse flow, the liquid rises in the venous and arterial chambers to the levels of the entrances of the inlets, and the amount of air in the chambers remains fixed, even after flow is reversed during normal operation with blood. Each of the arterial and venous chambers has a corresponding impermeable flexible diaphragm over a hole in a rigid wall of the chamber for the purpose of sensing pressure.
So-called “bottom entry” chambers whereby the blood inlet port is at the bottom of the chamber and blood enters into the blood space at the bottom or sidewall of the chamber are known from U.S. Pat. Nos. 4,681,606, 4,666,598 and European Patent No. 0058325.
Finally, U.S. Pat. No. 5,605,540 discloses a one-piece, plastic, blow molded arterial or arterial-venous blood chamber with bottom entry having equal height inlet and outlet wherein both the inlet and outlet have a progressively increasing cross section when moving from the bottom to the top of the chamber.
Furthermore the applicant has in the past put on the market air separators as schematically shown in appended FIGS. 7A and 8A.